I'm inspired by this to do a bit more planning for the "Spa Town Tour of the World" I've been thinking of ever since going to Baden-Baden some years ago. There really are a lot of potential stops.
Also, ever since sukitawdry suggested it ages ago, I've wanted to visit a jjimjilbang. There's been one in North Jersey for some years now which got a review in NJ Monthly a couple of years ago, a blogpost with lots of photos last spring and more recently a writeup in the Star-Ledger. Completely unsurprisingly, they run shuttles from Flushing and Manhattan.
Anyway, more hot tubbing. :)